Conventionally, both a molding machine and a molding process for simultaneously making an upper mold and a lower mold are well known. Both carry out the steps for defining a lower molding space by a lower squeezing board and a filling frame, introducing molding sand in an upper molding space and the lower molding space at the same time from a blow tank, lifting the lower squeezing board to simultaneously make an upper mold and a lower mold, removing them from a pattern plate, and removing the upper mold and the lower mold from a cope flask and a lower filling frame (see Patent Literature 1).
This conventional molding machine and molding process are implemented by, for instance, a hydraulically activated and pneumatically activated molding machine. However, such a molding machine involves the following problems. The hydraulic activation requires a hydraulic unit and thus increases the initial costs for a hydraulic pump and a hydraulic valve, while the pneumatic activation requires a larger cylinder to maintain sufficient power required by the setting flask and squeezing processes.
Under these circumstances, the applicant of the present application has conceived a combined driving mechanism that is a combination of pneumatic equipment and hydraulic equipment in the molding machine to use an air-on-oil system when cylinders are activated for a squeezing process and for switching pressures to drive the cylinder between a process for setting a flask and the squeezing process (see Patent Literature 2). As used herein, the term “air-on-oil system” refers to a plan for an operation to transform a pneumatic low-pressure to a hydraulic pressure to be used in the molding machine based on the hybrid functionality of the pneumatic pressure and the hydraulic pressure.
The driving mechanism described in Patent Literature 2, however, deals with no possibility of making the upper mold and the lower mold at the same time. Thus, it is unknown how to change the pressures of the air-on-oil system to be applied to the respective cylinders to appropriately operate the molding machine. Of course, Patent Literature 2 makes no mention of steps for removing the molds or for stacking the molds.
However, controlling adequate velocities and pressures are important matters for the step for removing molds or the step for stacking molds. For instance, in the step of removing molds, both removing the upper mold from an upper pattern and removing the lower mold from a lower pattern should be carried out slowly and gently. An inadequate control of the velocity results in molds with degraded qualities. A two-velocity control by the pneumatic pressure activation involves difficulties in adjusting the velocities, while a one-velocity control, which operates slowly, needs a significant operating time. In contrast, if the molds are removed at high velocities, it results in defective molded products, and a partial failure to remove the molds, called a “collapse of a sand mold.” Accordingly, molded products having high qualities cannot be obtained.
Similarly, in the step for stacking the molds, applying a high pressure or a high velocity to bring the produced upper mold and the produced lower mold close to each other often involves an impact on them that collapses or breaks them. Therefore, there is a possibility of producing defective molded products.